This invention relates to an X-ray diagnostic apparatus for producing transverse layer images of a subject, comprising an X-ray measuring arrangement including an X-ray source for generating a fan-shaped X-ray beam which penetrates the subject and of which the cross-section perpendicularly of the layer plane is equal to the layer thickness and, in the layer plane, is so great that the entire subject is penetrated, and a radiation receiver which determines the intensity of radiation behind the subject, which is in the form of a circular ring into which the subject can be introduced and has a series of detectors, and further comprising means for changing the direction of the axis of symmetry of the X-ray beam and comprising a computer for transforming the signals supplied by the radiation receiver into a layer image.
U.S. Pat. No. 3,778,614 describes an X-ray diagnostic apparatus which embodies all these features except for the circular radiation receiver. In this known X-ray diagnostic apparatus, the radiation receiver is laterally displaceable. When the subject is scanned, lateral displacements and rotational movements through a predetermined angle, for example one degree, follow one another in an alternating sequence until the entire subject has been scanned. The transducer includes a computer which calculates the transverse layer image from the measured absorption values. One disadvantage of this X-ray diagnostic apparatus is that the time required to form an image is relatively long on account of the necessary mechanical movement of the radiation detector and the X-ray tube.
An X-ray diagnostic apparatus of the kind referred to above is described in the publication entitled "Computerized Tomographic Scanner" of American Science and Engineering, Inc., Publication No. ASE-3869 April 1976. This X-ray diagnostic apparatus comprises a circular radiation receiver which surrounds the subject to be examined. Accordingly, it is only necessary to rotate the X-ray source, i.e. the radiation receiver does not have to be moved. Consequently, the time required to form an image is reduced in relation to the apparatus known from U.S. Pat. No. 3,778,614. Moreover, a simpler mechanical structure is also obtained.